"Windows XP Pro. Don't have access to the original drivers - they are part of a "system reboot" CD that came with the original machine."
I don't know XP but I am surprised by that statement. There should be a full set of drivers on the hard drive for PnP to work.
My first reaction would be to go to "add/remove hardware" and remove the two drives. Then re-boot and, if XP is anything like W2K, it will find the two drives and re-install them.
I've had a similar problem with Nero and my external CD/RW drive on a W2K machine and that's how I fixed it.